1. Field of the Invention
The present invention relates to a magnetic recording medium, and more particularly, to a magnetic recording medium affording both good electromagnetic characteristics and high reliability.
2. Discussion of the Background
As minicomputers, personal computers, and office computers such as work stations have become widespread in recent years, considerable research has been conducted in the field of magnetic recording into magnetic tapes (known as “data backup tapes”) for recording computer data as external memory media. The magnetic tapes that are employed for such applications are required to be of high reliability and capable of running stably for extended periods.
As the information that is being recorded has become more diverse and increased in quantity in recent years, data backup tapes with high recording capacities have been commercialized. Achieving a high recording capacity in a tape requires reducing the spacing between the magnetic layer and the magnetic head. For example, when large protrusions and indentations are present on the surface of the magnetic layer, a drop in output occurs due to spacing loss. This compromises electromagnetic characteristics by causing dropout, increasing the error rate, lowering the S/N ratio, and the like. Accordingly, it is necessary for the magnetic layer surface of a high-capacity data backup tape to be extremely smooth to achieve good electromagnetic characteristics.
In magnetic tapes, to lower the coefficient of friction, a backcoat layer having surface protrusions is widely provided on the opposite surface of the nonmagnetic support from the surface on which the magnetic layer is provided. Since magnetic tapes are normally wound up into rolls with cores, cassette hubs, or the like, the magnetic layer and the backcoat layer come into contact during the manufacturing process, during aging (thermoprocessing or the like), and during storage. This results in a phenomenon (known as “reverse transfer”) whereby the shape of the irregularities on the backcoat layer surface is transferred to the magnetic layer surface. Reverse transfer reduces the surface smoothness of the magnetic layer.
Accordingly, it would be conceivable to smoothen the surface of the backcoat layer to reduce reverse transfer. However, when the surface smoothness of the backcoat layer is increased, it becomes difficult to ensure running stability due to a rise in the coefficient of friction during manufacturing steps involving contact with the surface of the backcoat layer, the coefficient of friction with the drive system, and the like; failed winding due to accompanying air in the process of winding the magnetic tape; and the like.
Under these circumstances, by way of example, Reference 1 (Japanese Unexamined Patent Publication (KOKAI) Heisei No. 2-7223), Reference 2 (Japanese Unexamined Patent Publication (KOKAI) Heisei No. 2-141925), Reference 3 (Japanese Unexamined Patent Publication (KOKAI) Heisei No. 9-270115), Reference 4 (Japanese Unexamined Patent Publication (KOKAI) Heisei No. 9-115134), Reference 5 (Japanese Examined Patent Publication (KOKOKU) Heisei No. 4-81256), and Reference 6 (Japanese Unexamined Patent Publication (KOKAI) No. 2005-222644), which are expressly incorporated herein by reference in their entirety, propose the incorporation of two or more types of carbon black of differing average particle diameters into the backcoat layer as a countermeasure to reverse transfer.
However, even with the techniques described in References 1 to 6, it is difficult to obtain data backup tapes that afford good electromagnetic characteristics and can be employed for extended periods with high reliability.